Anyone has this problem also

Does anyone have a problem with the dust caps getting stolen from the valves on the wheels. I have replaced my dust caps around 3 or 4 times in the same bloody month...
Everytime i park up at the super market as this is the ONLY time the boxster is alone and they rape it..
i come back and my caps are always missing.. i have tried everything, even those anti theft ones but they still keep stealing them, it must be kids as they go missing 2 at a time, must be bmx bikes or something.. these caps are like £21.00 for a set of 4 and very shinny with a porsche crest in the middle. As soon as i see a kid with shinny caps on his bike i will get them back with a warning... the shinny caps must be what attracts them. Its a worrying fact that someone can do this and get away with it, wats to stop them scratching the car with a key or letting the tyres down.. anyways i have resulted back to basic black standard caps to try and stop this but again the little twats are stealing even them...

any ideas